Gate the whole of GEOlino Spezial behind the Welt 3 reward

It pointed at a 2020 episode, which locked the first handful and left the rest
of the show open - and the podcast retention cap has since deleted that episode
anyway, so the reward resolved to nothing at all.

An episode reward unlocks every episode up to and including the one named,
chronologically, so naming the newest covers the show: 356 of 356 episodes
locked until the lesson is passed, 0 after. Checked against the real library.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

roles/pi_musicmouse/files/tippen-curriculum.yml

@@ -371,8 +371,15 @@ worlds:
       - title: "Übung: Welt 3 komplett"
         subtitle: "Alles aus der unteren Reihe"
         drill: true
-        # Unlocks the first five episodes of GEOlino Spezial, oldest first.
-        unlocks: "Kinderpodcasts/GEOlino Spezial/20200323 - Das Immunsystem.mp3"
+        # Unlocks GEOlino Spezial. Naming the newest episode unlocks the whole show,
+        # because an episode reward unlocks every episode up to and including the one
+        # named (chronologically, oldest first) - so until this lesson is passed, the
+        # entire show is locked.
+        #
+        # An episode that arrives after this one is downloaded is newer than the named
+        # target, so it stays locked with nothing left to unlock it. Re-point this at
+        # the newest episode when that starts to matter.
+        unlocks: "Kinderpodcasts/GEOlino Spezial/20260901 - Der Vater der Chemie.mp3"
 
   - number: 4
     title: "Große Buchstaben"